Nonlinear control of the optical delay line pathlength

This paper discusses the problem of designing a control system for an interferometer delay line which contains coarse-vernier loops. The vernier loop compensator has nonlinear dynamics and includes a local feedback path containing a deadzone. This accomplishes two objectives: global stability and good transient response to large signals. In addition, by ensuring global stability in the vernier loop, the gain of the coarse loop may be increased thus providing greater disturbance rejection in the overall loop.